tFileStream读写之间循环时间差异巨大的原因是什么[重复]

Question

我尝试读取股票数据并将其写入文件。

相同的循环计数会产生巨大的差异。实际的写作循环大约需要 30 分钟。

这仅仅是因为驱动器写入速度的物理限制吗？

有什么方法可以改善写作过程吗？

uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, Vcl.StdCtrls, System.Generics.Collections;

type
  tSymbol = record
    CloseList: TList<Integer>;
    OpenList: TList<Integer>;
    VolumeList: TList<Integer>;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    ProgressBar1: TProgressBar;
    Memo1: TMemo;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    ReadList, WriteList: TList<tSymbol>;
  end;

procedure TForm1.Button1Click(Sender: TObject); // it takes 45 seconds.
var
  _FileStream: TFileStream;
  i, j: Integer;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  ProgressBar1.Min := 0;
  ProgressBar1.Max := 999;

  _FileStream := TFileStream.Create('test', fmCreate);

  for i := 0 to 999 do
  begin
    for j := 0 to 999 do
    begin
      _FileStream.Write(WriteList.List[i].CloseList.List[j], 4);
      _FileStream.Write(WriteList.List[i].OpenList.List[j], 4);
      _FileStream.Write(WriteList.List[i].VolumeList.List[j], 4);
    end;

    ProgressBar1.Position := i;
  end;

  _FileStream.Free;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.Button2Click(Sender: TObject); // it takes 6 seconds.
var
  _FileStream: TFileStream;
  _Close, _Open, _Volume: Integer;
  _Symbol: tSymbol;
  i, j: Integer;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  ProgressBar1.Min := 0;
  ProgressBar1.Max := 999;

  _FileStream := TFileStream.Create('test', fmOpenRead);

  for i := 0 to 999 do
  begin
    _Symbol.CloseList := TList<Integer>.Create;
    _Symbol.OpenList := TList<Integer>.Create;
    _Symbol.VolumeList := TList<Integer>.Create;

    for j := 0 to 999 do
    begin
      _FileStream.Read(_Close, 4);

      _Symbol.CloseList.Add(_Close);

      _FileStream.Read(_Open, 4);

      _Symbol.OpenList.Add(_Open);

      _FileStream.Read(_Volume, 4);

      _Symbol.VolumeList.Add(_Volume);
    end;

    ReadList.Add(_Symbol);

    ProgressBar1.Position := i;
  end;

  _FileStream.Free;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  _Symbol: tSymbol;
  i, j: Integer;
begin
  ReadList := TList<tSymbol>.Create;
  WriteList := TList<tSymbol>.Create;

  _Symbol.CloseList := TList<Integer>.Create;
  _Symbol.OpenList := TList<Integer>.Create;
  _Symbol.VolumeList := TList<Integer>.Create;

  for i := 0 to 999 do
  begin
    for j := 0 to 999 do
    begin
      _Symbol.CloseList.Add(0);
      _Symbol.OpenList.Add(0);
      _Symbol.VolumeList.Add(0);
    end;

    WriteList.Add(_Symbol);
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  ReadList.Free;
  WriteList.Free;
end;

Answer 1

使用缓冲文件 I/O。以较大的块读取/写入文件，根据需要管理每个块中的各个值。 Delphi 甚至在柏林 10.1 及更高版本中都有 TBufferedFileStream 类。

此外，在填充列表时，请提前预先分配列表的容量，以避免在向列表中添加新项目时必须重新分配列表的内部数组的开销。

试试这样的：

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, Vcl.StdCtrls, System.Generics.Collections;

type
  tSymbol = record
    CloseList: TList<Integer>;
    OpenList: TList<Integer>;
    VolumeList: TList<Integer>;
    constructor Create(InitialCapacity: Integer);
    procedure Cleanup;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    ProgressBar1: TProgressBar;
    Memo1: TMemo;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    ReadList, WriteList: TList<tSymbol>;
  end;

constructor tSymbol.Create(InitialCapacity: Integer);
begin
  CloseList := TList<Integer>.Create;
  CloseList.Capacity := InitialCapacity;

  OpenList := TList<Integer>.Create;
  OpenList.Capacity := InitialCapacity;

  VolumeList: TList<Integer>.Create;
  VolumeList.Capacity := InitialCapacity;
end;

procedure tSymbol.Cleanup;
begin
  CloseList.Free;
  OpenList.Free;
  VolumeList.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  FS: TFileStream;
  i, j, idx: Integer;
  Block: array of Int32;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  ProgressBar1.Position := 0;
  ProgressBar1.Min := 0;
  ProgressBar1.Max := 1000;
  ProgressBar1.Step := 1;

  FS := T{Buffered}FileStream.Create('test', fmCreate);
  try
    SetLength(Block, 3 * 1000);

    for i := 0 to WriteList.Count-1 do
    begin
      with WriteList[i] do
      begin
        idx := 0;
        for j := 0 to 999 do
        begin
          Block[idx+0] := CloseList[j];
          Block[idx+1] := OpenList[j];
          Block[idx+2] := VolumeList[j];
          Inc(idx, 3);
        end;    
      end;

      FS.WriteBuffer(Block[0], SizeOf(Int32) * Length(Block));
      ProgressBar1.StepIt;
    end;
    //FS.FlushBuffer;
  finally
    FS.Free;
  end;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  FS: TFileStream;
  Symbol: tSymbol;
  i, j, idx: Integer;
  Block: array of Int32;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  for I := 0 to ReadList.Count-1 do
    ReadList[I].Cleanup;
  ReadList.Clear;

  ProgressBar1.Position := 0;
  ProgressBar1.Min := 0;
  ProgressBar1.Max := 999;
  ProgressBar1.Step := 1;

  FS := T{Buffered}FileStream.Create('test', fmOpenRead or fmShareDenyWrite);
  try    
    SetLength(Block, 3 * 1000);
    ReadList.Capacity := 1000;

    for i := 0 to 999{(FS.Size div 12000) - 1} do
    begin
      FS.ReadBuffer(Block[0], SizeOf(Int32) * Length(Block));

      Symbol := tSymbol.Create(1000);
      try
        idx := 0;
        for j := 0 to 999 do
        begin
          Symbol.CloseList.Add(Block[idx+0]);
          Symbol.OpenList.Add(Block[idx+1]);
          Symbol.VolumeList.Add(Block[idx+2]);
          Inc(idx, 3);
        end;

        ReadList.Add(Symbol);
      except
        Symbol.Cleanup;
        raise;
      end;

      ProgressBar1.StepIt;
    end;
  finally
    FS.Free;
  end;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  Symbol: tSymbol;
  i, j: Integer;
begin
  ReadList := TList<tSymbol>.Create;

  WriteList := TList<tSymbol>.Create;    
  WriteList.Capacity := 1000;

  for i := 0 to 999 do
  begin
    Symbol := tSymbol.Create(1000);
    try
      for j := 0 to 999 do
      begin
        Symbol.CloseList.Add(0);
        Symbol.OpenList.Add(0);
        Symbol.VolumeList.Add(0);
      end;

      WriteList.Add(Symbol);
    except
      Symbol.Cleanup;
      raise;
    end;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
var
  i: Integer;
begin
  if ReadList <> nil then
  begin
    for i := 0 to ReadList.Count-1 do
      ReadList[i].Cleanup;
    ReadList.Free;
  end;

  if WriteList <> nil then
  begin
    for i := 0 to WriteList.Count-1 do
      WriteList[i].Cleanup;
    WriteList.Free;
  end;
end;

话虽如此，您可能会考虑将您的 3 个整数值合并到另一个 record 中，这样您就不会浪费时间和资源来分配这么多单独的列表：

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, Vcl.StdCtrls, System.Generics.Collections;

type
  tSymbolValues = record
    Close: Integer;
    Open: Integer;
    Volume: Integer;
  end;

  tSymbol = record
    Values: TList<tSymbolValues>;
    constructor Create(InitialCapacity: Integer);
    procedure Cleanup;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    ProgressBar1: TProgressBar;
    Memo1: TMemo;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    ReadList, WriteList: TList<tSymbol>;
  end;

constructor tSymbol.Create(InitialCapacity: Integer); 
begin
  Values := TList<tSymbolValues>.Create;
  Values.Capacity := InitialCapacity;
end;

procedure tSymbol.Cleanup;
begin
  Values.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  FS: TFileStream;
  i, j, idx: Integer;
  Block: array of Int32;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  ProgressBar1.Position := 0;
  ProgressBar1.Min := 0;
  ProgressBar1.Max := 1000;
  ProgressBar1.Step := 1;

  FS := T{Buffered}FileStream.Create('test', fmCreate);
  try
    SetLength(Block, 3 * 1000);

    for i := 0 to WriteList.Count-1 do
    begin
      with WriteList[i] do
      begin
        idx := 0;
        for j := 0 to Values.Count-1 do
        begin
          with Values[j] do
          begin
            Block[idx+0] := Close;
            Block[idx+1] := Open;
            Block[idx+2] := Volume;
            Inc(idx, 3);
          end;
        end;    
      end;

      FS.WriteBuffer(Block[0], SizeOf(Int32) * Length(Block));
      ProgressBar1.StepIt;
    end;
    //FS.FlushBuffer;
  finally
    FS.Free;
  end;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  FS: TFileStream;
  Symbol: tSymbol;
  Values: tSymbolValues;
  i, j, idx: Integer;
  Block: array of Int32;
begin
  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));

  for I := 0 to ReadList.Count-1 do
    ReadList[i].Cleanup;
  ReadList.Clear;

  ProgressBar1.Position := 0;
  ProgressBar1.Min := 0;
  ProgressBar1.Max := 999;
  ProgressBar1.Step := 1;

  FS := T{Buffered}FileStream.Create('test', fmOpenRead or fmShareDenyWrite);
  try    
    SetLength(Block, 3 * 1000);
    ReadList.Capacity := 1000;

    for i := 0 to 999{(FS.Size div 12000) - 1} do
    begin
      FS.ReadBuffer(Block[0], SizeOf(Int32) * Length(Block));

      Symbol := tSymbol.Create(1000);
      try
        idx := 0;
        for j := 0 to 999 do
        begin
          Values.Open := Block[idx+0];
          Values.Close := Block[idx+1];
          Values.Volume := Block[idx+2];
          Symbol.Values.Add(Values);
          Inc(idx, 3);
        end;

        ReadList.Add(Symbol);
      except
        Symbol.Cleanup;
        raise;
      end;

      ProgressBar1.StepIt;
    end;
  finally
    FS.Free;
  end;

  Memo1.Lines.Add(FormatDateTime('hh:mm:ss', Time));
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  Symbol: tSymbol;
  Values: tSymbolValues;
  i, j: Integer;
begin
  ReadList := TList<tSymbol>.Create;

  WriteList := TList<tSymbol>.Create;    
  WriteList.Capacity := 1000;

  for i := 0 to 999 do
  begin
    Symbol := tSymbol.Create(1000);
    try
      for j := 0 to 999 do
      begin
        Values.Open := 0;
        Values.Close := 0;
        Values.Volume := 0;
        Symbol.Values.Add(Values);
      end;

      WriteList.Add(Symbol);
    except
      Symbol.Cleanup;
      raise;
    end;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
var
  i: Integer;
begin
  if ReadList <> nil then
  begin
    for I := 0 to ReadList.Count-1 do
      ReadList[i].Cleanup;
    ReadList.Free;
  end;

  if WriteList <> nil then
  begin
    for I := 0 to WriteList.Count-1 do
      WriteList[i].Cleanup;
    WriteList.Free;
  end;
end;